We demonstrate the direct photolithographic patterning of a grossly nonplanar substrate by creating 62-m helical tracks on a 22- mm-high cone. The projection of focused light onto the 3-D surface is achieved using a computer-generated hologram CGH suitably illumi- nated so as to create the required pattern on the photoresist-coated surface. The approach adopted forms the basis of a novel method for patterning nonplanar structures. We address the key challenges encoun- tered for the implementation of holographic photolithography in three dimensions, including mask design and manufacture, exposure compen- sation, mask alignment, and chemical processing. Control of linewidth and resolution over the nonplanar surface is critical. We describe the methods adopted and critically assess the structures created by this pro- cess. The bihelical cone is representative of a broadband, high- frequency coil-like structure, known in wireless communications as a log- periodic antenna. © 2007 Society of Photo-Optical Instrumentation Engineers.